1.1 Technical Field.
This invention pertains to mining rock or ore from an ore body located below the surface of the ground.
1.2 Background Art.
The extraction of ore from beneath the surface of the ground may be accomplished by a number of different mining methods. Mining techniques based on caving are typically useful for types of ore which will fracture into fragments, such as copper, molybdenum, and silver. Caving methods rely on the removal of rock support beneath ore bodies, causing ore and rock to fragment and subside, facilitating the removal of ore fragments and rock wastes.
Traditional caving methods involve the creation of numerous horizontal work areas, known as drifts, in the area of an ore body. Each drift may have a separate purpose. For example, a caving method utilized for steeply dipping tabular ore bodies may involve an uppermost drift, closest to the surface of the earth, created for the purpose of causing the ore to cave downward from above the drift into an area from which it can be collected. A second drift may be blasted to permit access by vehicles designed to collect and push the ore to a vertical tunnel, or finger raise, where it is lowered to a haulage drift. In the haulage drift, a train system may be utilized to pull the ore back to the surface of the earth. Yet another drift may be utilized to provide ventilation for the mining system. This model of mining is typically referred to as sublevel caving.
A caving technique known as block caving relies on creation of a principal haulage drift, from which finger raises extend upward to a production level. More finger raises are then driven upward to a level from which caving is initiated by drilling and blasting a block of ore. Once an initial block of ore has been removed, the ore above caves under its own weight, forcing crushed fragments of the ore to flow through the finger raises.
These traditional caving methods have a number of important advantages. Although initial construction costs of mines based on caving are usually high, the cost of operating the mines is relatively inexpensive. Once started by drilling and blasting, caving relies primarily on gravity for its operating efficiency, as rock is fragmented without further energy input. These processes prove particularly useful for recovering large, deep, low grade ore bodies. Nevertheless, traditional caving methods have a unique set of disadvantages as well. If caving does not proceed at a consistent rate, bridging may occur as solid ore forms an arch over the cave. No further flow of ore occurs until the arch is broken. Expensive and time-consuming measures may be required to remedy the effects of sporadic bridging. This process is particularly dangerous since abrupt failure of the arch can occur.
A modified caving method is disclosed in Janelid U.S. Pat. No. 4,072,352. Parallel and horizontal drifts are driven, at several levels, into the lower part of a block of ore. The drifts are arranged so that the drift openings form a stepped configuration. Caving is accomplished by blasting an area of ore to undercut a portion of the ore body above drift openings. As openings become damaged or blocked, new draw points may be established through retreat allowing ore removal to continue further back in the same drift.
Smith U.S. Pat. No. 2,298,599 teaches a modified block caving design. Through the use of inclined drifts and a conveyor deck, access to drawpoints is simplified to permit ease of ore removal by mechanical conveyors. Unlike traditional block caving methods, the Smith design does not rely on gravity flow.
Yet another variation of traditional mining techniques is described in Bucky U.S. Pat. No. 2,536,869. The Bucky method is oriented to mining weak ore from narrow, tabular ore bodies, with strong surrounding country rock. Ore is broken in a sloped stope area, and waste fill is introduced at the top of the stope to promote continuous flow of the ore through the stope.
Each of these mining designs is particularly useful for removal of specific types of ore found in ore bodies of a certain shape. Although each design known in the prior art has express advantages, none of these models is configured to conform in three dimensions to the shape of the relevant ore body. Thus, each known mining design must be altered to respond to practical differences in the configuration of each ore body. Furthermore, each known caving technique is susceptible to bridging, resulting in significant mining delays.